My actual position on this matter is even more radical. I am against any tutoring at all by students. Practice time is sacred and most valuable and should not be wasted by talking. Our purpose is to practice not to teach. We just follow the Sensei's example and try to emulate his technique as good as we can. If he finds any substantial flaw, he will come to correct it, otherwise he will let you fine-tune your technique by practice.

I have a principle NEVER to teach my partner even when he's doing wrong. And I don't want anyone to teach me even if I'm doing all wrong. There is a teacher whose duty is this very task, so leave it up to him.

Now since some people feel a great urge to teach no matter what, I prefer that they teach by action and example. If they start to talk, I just say shut-up and practice. Of course it's not a silent movie, and the partner could say for instance: "Would you like to try it this way?" but that's just about all what I tolerate. Lengthy explanations are not welcome.

I leave the technical discussion and speculation for the beer session after the class.